Chain drive tensioner assemblies are used to operate ancillary components associated with automotive engines. For example, chain drive tensioner assemblies are used to drive complex valve trains, balance shafts, oil pumps, high pressure fuel injection pumps and water pumps.
Known chain drive tensioner assemblies include a chain and a chain drive tensioner system that is operable to create an initial required tension on the chain. Known chain drive tensioner assemblies generally include a tensioner body and a tensioner piston attached to a shoe. Oil pressure within a hydraulic chamber of the tensioner body exerts pressure against the tensioner piston and shoe assembly, which engages the chain to create the required tension. Under impact forces from the chain, some oil leaks from the hydraulic chamber along an oil leakdown path with an orifice of fixed size. The stiffness of the chain drive tensioner assembly is controlled by the amount of oil leakage allowed from the hydraulic chamber. Increased tensioner stiffness leads to improved chain drive control. However, as oil temperature is increased, the viscosity of oil in the hydraulic chamber is decreased, and thus more oil leaks out of the leakdown path, decreasing stiffness of the assembly. When the oil temperature is relatively low, viscosity increases and therefore less oil can leak out of the fixed orifice leakdown path, increasing stiffness of the tensioner assembly and potentially causing the tensioner to experience “pump up” (i.e., an over-extension of the piston and shoe) which decreases chain drive control.